1078 
Soth of auricle and ventricle the halving of the rhythm can also 
suddenly oceur (i.e. with regard to the sinus-contractions). 
After this rhythm-halving the a-v-interval is shortened again, the 
irritability of the ventricle has improved: an extra-stimulation during 
the diastole causes again an extra-systole, but now without compen- 
satory pause; the row of the ventricle-curves has only been removed 
by one auricle-systole. Tbe duration of this extré-period + the duration 
of the preceding period is now equal to the duration of 1*/, heart- 
periods. : 
When now this halved rhythm of the ventricle has existed for ¢ 
short time, I can, with one induction-stroke during the diastole, 
reduce this rhythm to the original one, which can continue again 
for some time: consequently an artificial return to the original 
rhythm. This experiment can be explained as follows: Im the first 
place it is irrefutable, that the metabolic condition of the heartmuscle 
was such as to allow the heart to pulsate in the normal rhythm; 
nor were the physiological irritations proceeding from the auricle 
wanting, for only the ‘ventricle pulsated in the halved rhythm; and 
yet this halved rhythm would have continued, if I had not intervened 
by an extra-stimulation. The cause of this phenomenon is, that the 
systoles of the halved type are much larger and wider than those 
of the not halved one. Each systole in itself of the halved type has 
consequently a larger refractory period, so that each second auricle- 
systole cannot be answered by the ventricle. The ventricle is conse- 
quently, as it were imprisoned in its own rhythm; if there were 
enly one narrower systole with a smaller refractory period between, 
then the normal rhythm would have been restored with the smaller 
systoles. Now I obtain this little systole as an answer to the extra- 
stimulation, and because the latter took place directly after an auricle- 
systole, the extra-systole is not followed by a compensatory pause, 
but after the extra-stimulation I detect a continual recovery of the 
original rhythm. If the extra-systole was foliowed by a compensatory 
pause, this recovery of the rhythm could not take place, for the 
postcompensatory systole would have been enlarged (= widened) 
again, and would thus restore again the halved rhythm. At the same 
time we have here consequently before us an example of an extra- 
systole without a compensatory pause. The ventricle can thus again 
pulsate e. g. about 5 minutes in the original rhythm and then pass 
again in the ordinary way into the halved rhythm. During the first 
time of halving the metabolic condition of the heartmuscle had 
certainly much improved, but every large systole of this type has 
in itself a larger refractory period than every little systole of the 
